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A182676 a(n) is the largest n-digit number with exactly 8 divisors, a(n) = 0 if no such number exists. 1
0, 88, 999, 9994, 99995, 999994, 9999994, 99999994, 999999998, 9999999995, 99999999998, 999999999998, 9999999999998, 99999999999998, 999999999999995, 9999999999999998, 99999999999999998, 999999999999999987, 9999999999999999995 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = the largest n-digit number of the form p^7, p^3*q or p*q*r (p, q, r = distinct primes), a(n) = 0 if no such number exists.

LINKS

Table of n, a(n) for n=1..19.

FORMULA

a(n) = max {10^(n-1) <= k < 10^n : A000005(k)=8} if set is nonempty, else a(n) = 0.

MAPLE

with (numtheory):

a:= proc(n) local k;

     if n<2 then 0

   else for k from 10^n-1 while tau(k)<>8 by -1

        do od; k

     fi

    end:

seq (a(n), n=1..20);

PROG

(PARI) a(n)=forstep(k=10^n-1, 10^(n-1), -1, numdiv(k)==8 & return(k)) \\ M. F. Hasler, Nov 27 2010

CROSSREFS

Cf. A000005, A182675.

Sequence in context: A227479 A321061 A295591 * A228744 A249294 A239274

Adjacent sequences:  A182673 A182674 A182675 * A182677 A182678 A182679

KEYWORD

nonn,base

AUTHOR

Jaroslav Krizek, Nov 27 2010

EXTENSIONS

Edited by Alois P. Heinz, Nov 27 2010

Given terms double-checked with given PARI code by M. F. Hasler, Nov 27 2010

STATUS

approved

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Last modified September 25 10:50 EDT 2022. Contains 356978 sequences. (Running on oeis4.)